This invention relates to an apparatus for optical detection of sheet material such as bank notes or papers of value.
DE 195 17 194 A1 discloses an apparatus with a stationary detection device for detecting the light of an area of the sheet material incident from the direction of a detector axis and emitted in the direction of an optical sheet material axis. For optical detection the sheet material is transported past the stationary detection device along a transport direction. The area detected by the detection device comprises the total width of the sheet material perpendicular to the transport direction so that the total surface of the sheet material is detected when it is transported past.
In addition, an illumination device is provided for illuminating the sheet material during detection. The illumination device has components for illuminating the sheet material from both sides so that the detection device can detect both reflected and transmitted light.
The resolution of the apparatus is about 50 dpi. For certain applications, such as the detection of a bank note number on a bank note by means of optical character recognition (OCR) software, this resolution is deficient. Increasing the resolution to about 250 dpi, e.g. for detecting a bank note number, leads to very high data rates which are about a factor of 25 higher than the data rates of the known apparatus. The problem here is that such data rates can only be processed with high effort, if at all.